import pygame
from pygame.sprite import Sprite


class Ship(Sprite):

    def __init__(self, settings, screen):
        """
        初始化飞船，并设置其初始位置
        """
        super().__init__()

        self.screen = screen
        self.settings = settings

        # 加载飞船图像并获取其外接矩形
        self.image = pygame.image.load("images/ship.bmp")
        self.rect = self.image.get_rect()
        self.screen_rect = screen.get_rect()

        # 将每艘飞船放到屏幕底部中央
        self.rect.centerx = self.screen_rect.centerx
        self.rect.centery = self.screen_rect.centery
        self.rect.bottom = self.screen_rect.bottom

        # 在飞船的center属性中存储小数值
        self.center_x = float(self.rect.centerx)
        self.center_y = float(self.rect.centery)

        # 移动标志
        self.moving_up = False
        self.moving_down = False
        self.moving_left = False
        self.moving_right = False

    def blit_me(self):
        """
        指定位置绘制飞船
        """
        self.screen.blit(self.image, self.rect)

    def update(self):
        """
        根据移动标志调整飞船的位置
        """
        if self.moving_up and self.rect.top > 0:
            self.center_y -= self.settings.ship_speed_factor

        elif self.moving_down and self.rect.bottom < self.screen_rect.bottom:
            self.center_y += self.settings.ship_speed_factor

        elif self.moving_left and self.rect.left > 0:
            self.center_x -= self.settings.ship_speed_factor

        elif self.moving_right and self.rect.right < self.screen_rect.right:
            self.center_x += self.settings.ship_speed_factor

        self.rect.centery = self.center_y
        self.rect.centerx = self.center_x

    def center_ship(self):
        """
        让飞船在屏幕上居中
        """
        self.center = self.screen_rect.centerx
